The present invention relates generally to heat exchange coils, and more particularly to a finned tube heat exchanger coil having plate fins including a lanced sine-wave heat transfer surface for use in heating, ventilation, and air-conditioning and a method for manufacturing thereof.
Plate fins utilized in the air conditioning and refrigeration industry are normally manufactured by progressively stamping a coil of plate fin stock and then cutting the stamped fin to the desired length. The fins are then collected in the proper orientation and number in preparation for forming a coil. Previously formed hairpin tubes are then inserted through openings within the fins and thereafter expanded to form a mechanical and thermal connection between the tubes and fins. The open ends of the hairpin tubes are fluidly connected by way of U-shaped return bends, and subsequently the return bends are soldered or brazed in place. The plate fins are typically manufactured in either a draw or drawless die to form both the fin shape as well as surface variations on the fin and openings through which the tubular members are inserted.
Generally, the HVAC industry presently forms a plurality of rows of fins simultaneously from a section of plate fin stock. These rows of fins are cut to the desired number of rows for the coils and are then collected on stacking rods or within a box or some other means to form a pile or stack of fins ready to be laced with hairpin tubes to form the coil.
Prior art fins are provided with a variety of surface variations or enhancements to improve the transfer of heat energy between the fluids passing through the tubular members and over the plate fin surfaces. These enhanced fins are either flat fins or wavy fins. Flat fins are generally enhanced by manufacturing raised lances therein. A raised lance is defined as an elongated portion of fin formed by two parallel slits whereby the stock between the parallel slits is raised from the surface of the fins stock. Wavy fins, in addition to having raised lances, may also have louvered enhancements. A louver is defined a section of fin stock having one elongated slit wherein the surface of the fin stock on one side of the slit is raised from the surface of the stock.
Generally, enhanced wavy fins either have a raised lance or a louver at both the leading and trailing edges. Enhanced fins with raised lances at the edges are weak and non-rigid along the edges due to the surface enhancement thereon. Enhanced wavy fins with louvers at the leading and trailing edges have very steeply inclined surfaces at the edges and cause excessive pressure drop due to the steep angle of inclination.
Thus, there is a clear need for an enhanced plate fin surface which has strong leading and trailing edges, and also eliminates the very deep trough which contributes to excessive pressure drop.